Chimeric Antigen Receptor T-Cell Therapy Associated Cerebral Glucose Hypometabolism (CART-CGHM): A Novel Cerebral Metabolic Complication

Introduction:

CAR-T (chimeric antigen receptor T-cell) therapy is known to be associated with immune-mediated toxicities including cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). [¹⁸F]-Flurodeoxyglucose-positron emission tomography (FDG-PET) is frequently utilized for cancer staging before and after CAR-T therapy. Case series have demonstrated cerebral glucose hypometabolism (CGHM) on FDG-PET imaging in patients who developed CRS and ICANS. In this study, we aim to further characterize CART-CGHM.

Methods:

Patients who received CAR-T therapy at our institution from October 2019 to December 2023 were included. Clinical data was collected from retrospective review of the electronic medical record including patient age, sex, diagnosis, cancer stage, development of CRS or ICANS, and survival outcome.

Standard of care whole body FDG-PET scans obtained before and approximately 30 days post CAR-T therapy were utilized. FDG-PET images of the brain were sub-selected and processed with dedicated imaging software (GE AW server 3.2 with Cortex ID, MIM Neuro, version 7.2.7). To identify CART-CGHM, visual and statistical comparison was made between the pre-CAR-T FDG-PET and the post-CAR-T FDG-PET using the age and gender matched normal cohort in the database as controls. Z-score changes > 1.5 were considered significant.

Baseline variables were reported as frequency (%) and compared between patients with and without CGHM using Chi-squared test. Kaplan-Meier method was used to estimate the overall survival rate (OS) at different time points and log rank test was used to compare survival rates between the groups with and without CGHM. Multivariable Cox regression model was performed to evaluate the association between CGHM and OS with adjustment for ICANS. All tests were two-sided with p<0.05 considered statistically significant.

Results:

In total, 84 patients (41 women, 49%) were included. The median age at time of CAR-T therapy was 66 (33-85) years old. The most common diagnosis was multiple myeloma (n=39, 46%) followed by diffuse large B-cell lymphoma (n=33, 39%), follicular lymphoma (n=7, 8%), mantle cell lymphoma (n=3, 4%), and B-cell acute lymphoblastic leukemia (n=2, 2%). CART-CGHM was identified in 27 patients (32%). The pattern of CGHM was either global (n=15, 56%) or focal (n=12, 44%) with the prefrontal cortex predominantly affected. Of these 27 patients with CART-CGHM, 17 patients (63%) experienced ICANS and 23 patients (85%) experienced CRS. The diagnosis of lymphoma and development of ICANS were significantly associated with CGHM (p- 0.038 and <0.001 respectively). On univariate analysis, CGHM and ICANS were associated with negative impact on OS. The post-CAR-T 12-month OS for patients with CGHM was 76% versus 84% without CGHM (p-0.016), and 12-month OS for patients with ICANS was 64% versus 91% without ICANS (p-0.001). The post-CAR-T median OS for patients with CGHM, patients with ICANS, and patients with both CGHM and ICANS were 17.1 months, 13.5 months, and 12.6 months, respectively. On multivariate analysis, after adjusting for ICANS, CGHM alone did not have an impact on OS [HR 1.76 (0.71, 4.37); p-0.2250] but ICANS continued to have a negative impact on OS [HR 3.03 (1.21, 7.57); p-0.0178].

Conclusions:

Our study represents the largest study to date on CART-CGHM. CART-CGHM was seen in 32% of CAR-T patients and had a strong association with ICANS and lymphoma patients. ICANS was found in 63% of CART-CGHM patients. ICANS alone or CGHM with ICANS were associated with a negative impact on OS. Although the underlying biological mechanism of CART-CGHM is not clear, it likely represents a significant immune-mediated reduction in cerebral glucose uptake. We suggest that CGHM represents a novel metabolic complication of CAR-T therapy and significantly contributes to CAR-T therapy associated neuro-cognitive toxicity. Although CART-CGHM can resolve completely, our study also showed patients with persistent CGHM on post-CART follow up FDG-PET scans. As such, CART-CGHM can potentially result in chronic neuro-cognitive complications. The current therapeutic interventions for CRS and ICANS do not appear to be adequately effective for CART-CGHM. Further research, involving multiple institutions, is urgently needed for better understanding of CART-CGHM and to develop specific therapeutic interventions.